Group III-V compound semiconductors, such as GaN, AlGaN, etc., have several advantages, namely, wide and easily adjustable bandgap energy, and are thus widely used in optoelectronics and for electronic elements.
Particularly, light emitting devices, such as light emitting diodes (LEDs) or laser diodes, which use group III-V or II-VI compound semiconductor materials, are capable of emitting visible light of various colors, such as red, green and blue, and ultraviolet light owing to development of element materials and thin film growth techniques, are also capable of emitting white light with high luminous efficacy through use of phosphors or by combining colors, and have several advantages, namely, low power consumption, semi-permanent lifespan, fast response speed, safety, and environmental friendliness, as compared to conventional light sources, such as fluorescent lamps and incandescent lamps.
Accordingly, application of the light emitting devices has been extended to transmission modules of optical communication means, light emitting diode backlights to replace Cold Cathode Fluorescent Lamps (CCFL) which serve as backlights of Liquid Crystal Display (LCD) apparatuses, white light emitting diode lighting apparatuses to replace fluorescent lamps or incandescent lamps, vehicle head lamps, and traffic lights.
A molding unit protecting a light emitting structure or wires may be arranged around a light emitting device and, when light passes through the molding unit formed of a material, such as silicone, the light is refracted by the molding unit and thus the molding unit may function as a primary lens.
However, when the light emitting device is used a light source of a lighting apparatus, a secondary lens may be used to adjust a light emission path and the secondary lens is generally referred to as a ‘lens’.
A light path may be greatly changed according to materials of the lens, particularly, shapes of the lens, and, particularly, in an application, such as a streetlamp which causes light emitted by a light source to proceed only in a specific direction, i.e., a forward or backward direction, the shape of the lens is more important.
A lighting apparatus used as a streetlamp must concentrate light on a street side rather than a house side and a security light used as a lighting apparatus in a designated space must have excellent luminance in a central region thereof, but these lighting apparatuses must have a designated level of uniformity in edge regions thereof.